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LECTURES 



ON 



actRicultural chemistry, 



DELIVERED BEFORE THE SENIOR CLASS 



UNIVERSITY OF GEORGIA, 



BY JOHN LeCONTE, M. D., 



Professor of Natural Philosopiy acd Chemistry. 



PUBLISHED BY REQUEST OF THE CLASS. 




ATHENS, GA. 

PRINTED BY CHRISTY to LAMPKi:^. 
1847. 




6^ 






CORRESPONDENCE. 



Franklin College, Oct. 23d, 1847. 
Sir — ^We have been appointed a committee by the Senior Class to tender 
you their sincere thanks for the politeness and respect you have on all occa- 
sions manifested towards them, and also to solicit for publication copies of 
vour Lectures on Agricultural Chemistry, read before them on the evenings 
of the 21 St and 22d instant. 

Ardently desiring that you ■will comply -with our request, ^ve return you 
the highest esteem of the Class and the warmest regard of 
Your humble servants, 

W. D. WILLIAMS, 1 

J. M. TILLEY, I ^ .,, 

F. R. TARVER, ^ ^ommuiee. 

Dr. Jxo. LeConte. B. A. THORNTON, 



Athens, Oct. 25th, 1847. 

Gentlemen — -In reply to your communication of the 23d instant, in 
behalf of the Senior Class, I beg that you would return to the members of 
the Class my warmest acknowledgments for the uniform respect and atten- 
tion they have shown me, and for the very flattering manner in which they 
have seen fit to express themselves. 

Under the circumstances, I feel bound to place the Lectures referred to at 
the disposal of the Class ; although the)' contain nothing that is new, or 
that is not accessible to those who ba7'2 kept pace with the advancement of 
this department of Science. 

With sentiments of the highest esteem, I remain yours, very truly, 
To Messrs. JOHN LeCONTE,' 

W. D. WlLLLVMS, ] 
J. M. TiLLEV, ." ^ 

F.R.Tauver, \Commttlee.- 
B. A. Tuorkton. J 



r 



5 LECTURE L 



The most careless observer cannot fail to reco2:nIze in 
the world around him, many evident distinctions between 
living beings and inanimate objects. Perhaps the most ap- 
parent and permanent of these distinctions is based rather 
upon a comparison of their mode of existence, than upon 
any examination of their intimate structure. The ceaseless 
tendency to change, manifested in the life of the tbrmer, 
stands in yet more obvious contrast with the unaltering 
stahility of the latter. The snow-capped mountain rears its 
summit to the clouds, unaffected by the lapse of the ages 
which have rolled by since its first elevation — a monument 
of Nature's power ; and the giant edifices erected by the 
hand of man on the plains of Egj'pt, bear to remote poster- 
ity the attestation of the former grandeur of a nation now 
sunk in poverty and insignificance. And what, compared 
With the permanence of these, is the duration of any struc- 
ture subject to the conditions of vitality ? 'V.o be born, to 
grow, to arrive at maturity, to decline, to flic, to decav-, is 
the sum of the history of every being that lives, from man 
in the pomp of roN^aliy or the pride of philosophy, to the 
gay and thoughtless insect that glitters for a few liours in 
the sunbeam and is seen no more ; from the staleh^ oak, 
the monarch of the forest through successive centuries, to 
the humble fungus which shoots forth and withers in a day. 
And \'et, amidst the constant change and succession of in- 
dividuals, we observe the form and character first impressed 
upon each race by the Creator of all, uninterruptedly trans- 
milted from parent to offspring through periods of indeli- 
nite duration. " One generation passelh away" — but " an- 
other Cometh" — like it in structure, functions, habits, food, 
instincts, passions, and the limit of its existence. The mis- 
letoe flourishes on the oak of the English forests, just as 
when made an, object of superstitious veneration in the hal- 
lowed groves of the Druids. The l>ee builds her comb with 
the same uiwarying regularity, and stores it with the snme 
materials now, as wheti her beautiful works attracted the 



notice of the poets and philosophers of classic ages. And 
man, however modified by education, however various his 
degree of civilization, however elevated his condition of 
mental-and moral refinement, is yet born the same helpless 
dependent being, with the same dormant faculties of body 
and mind, as the first offspring of our original parents. 

In the ever-varying conditions of the animated world, 
(hen, a very superficial glance will display to us a certain 
degree of regularity and arrangement ; and the more atten- 
tively we investigate the relations which its changes present, 
the more stable and definite is the assurance we obtain, 
that they are all harmonized and controlled by fixed laws, 
which are but simplified expressions of those conditions of 
action which the Creator has imposed upon organized no 
less than inorganic matter. To arrive at a knowledge of 
these laws, and, having attained them, to trace their appli- 
cation to all the countless variety of phenomena presented 
by the myriads of living beings whose beautiful forms peo- 
ple this globe, is the object of the science of Ph3^siology — the 
science of life — using that term in its most extended sense. 
Only ^ port of this immense field of investigation appropri- 
ately belongs to the chemist. " The object of organic chem- 
istry is to discover the chemical conditions which are essen- 
tial to the life and perfect development of animals and 
vegetables, and, generally, to investigate all those processes 
of organic nature which are due to the operation of chemi- 
cal laws." — Licbig. 

I propose, on this occasion, to take a rapid and cursory 
survey of a few of the discoveries which chemistry has fur- 
nished within the last 6 or 8 years, viewed in their re- 
lation to agriculture. During the last few months, you 
have learnt liiat, all the material substances m nature con- 
sist of one or more of 55 or 60 elementary bodies. This is 
sufficiently surprising, j^et it is, if possible, still more re- 
markable that nearly the entire mass of every vegetable and 
animal substance may be resolved into one or more o^four 
only of these simple substances. I say nearlij the entire 
mass, because inorganic matters do enter into the constitu- 
ents of both animals and vegetables, and are essential to 
iheir perfect development; but they constitute but a com- 
paratively small portion of their bulk. When a portion of 
animal or vegetable matter is burned, it either entirely dis- 
appears or leaves behind it only a small quantity of ashes. 
JNow all that disappears in this process, generally consists 
of 4 elementary bodies, viz: carbon, oxygen, hydrogen and 



nitrogen. To the agriculturist, therefore, an acquain- 
tance with these 4 constituent parts of all that lives and 
grows on the face of the globe, is absolutely indispensable. 
It is impossible for him to comprehend the laws by which 
the operations ol nature in the vegetable kingdom are con- 
ducted, or the reason ot the processes he himself adopts in 
order to facilitate or to modify these operations, without 
this previous knowledge of the nature ot the elements — the 
raw materials as it were, out of which all the products of 
vegetable growth are elaborated. — Johistoii's Lectures on 
Agricultural Che)nistr)j. 

Presuming that you have a sufficient general acquain- 
tance with these organic elements, we will pass on imme- 
diately to the subject of Agriculture. 

Agriculture is both a science and an art. The knowl- 
edge of all the conditions of the life of vegetables, the ori- 
gin of their elements, and the sources of their nourishment, 
forms its scientific basisr From this knowledge we derive 
certain rules for the exercise of the art, the principles upon 
which the mechanical operations of farming depend, the 
usefulness or necessity of these for preparing the soil to 
support the growth of plants, and for removing every ob- 
noxious influ(3nce. No experience, drawn from the exer- 
cise of the art, can be opposed to true scientific principles, 
because the latter should include all the results of practical 
operatiotis, and are in some instances solely derived there- 
from. Theory must correspond with experience, because 
it is nothing more than a reduction of a series of phenomena 
to their last causes. A field in which is cultivated the same 
plant for several successive years, becomes barren for that 
plant in a period varying with the nature of the soil : in one 
field it will be in 3, in another in 7, in a third in 20, in a 
fourth in 100 years. One field bears wheat, and no peas ; 
another beans and turnips, but no tobacco; a third gives a 
plentiful crop of turnips, but will not bear clover. Whatis 
the reason that a field loses its fertility for one plant, the 
same \vhich at first flourished there? Whatis the reason 
one kind of plant succeeds in a field where another fails? 
These questions belong to science. What means are neces- 
sary to preserve to a field its fertility for one and the same 
plant? What to render one field fertile for two, for three, 
for all plants ? These last questions are put by art, but 
they cannot be answered by art. If a farmer, without the 
guidance of just scientific principles, is trying experiments 
to render a field fertile for a plant which it otherwise will 



not bear, his prospect ot success is very small. Thousands 
of farmers try such experhnents in various directions, the 
result of which is a mass of practical experience forming a 
method of cultivation which accomplishes the desired end 
for certain places; but the same method does not succeed 
— it indeed ceases to be applicable to a 2d or 3d place in 
the immediate neighborhood. How large a capital, and 
how much power, are wasted in these experiments! Very 
different, and far more secure, is the path indicated by sci^ 
ence ; it exposes us to no danger of failing, but, on the con- 
trary, it furnishes us with every guarantee of success. If 
the cause of failure, of barrenness in the soil for one or two 
plants, has been discovered, means to remedy it may read- 
ily be found. — Liebig's Letters. 

The most exact observations prove that the method of 
cultivation must vary with the geological condition of the 
subsoil. In basalt, porph}^-}'', sandstone, limestone, etc., 
are certain elements indispensable to the growth of plants, 
and the presence of which renders them fertile. This fully 
explains the difference in the necessary methods of culture 
for different places ; since it is obvious that the essential 
elements of the soil must vary with the varieties of compo- 
sition of the rocks, from the disintegration of which they 
originated. Wheat, corn, clover, turnips, for example, 
each require certain elements from the soil ; they w-ill not 
flourish where the appropriate elements are absent. Science 
teaches what elements are essential to every species ot 
plant by an analysis of their ashes. If, therefore, a soil is 
found wanting in any of those elements, we discover at once 
the cause of its barrenness, and its removal may now be 
readily accomplished. The empiric attributes all his suc- 
cess to the mechanical operations of agriculture ; he expe- 
riences and recognises their value, without inquiring what 
are the causes of their utilit}', their mode of action : yet this 
scientific knowledge is of the highest importance for regu- 
lating the application of power and the expenditure of cap- 
ital — for insuring its economical expenditure and the pre- 
vention of waste. Can it be imagined, that the mere passing 
of the ploughshare or the harrow through the soil— the mere 
contact of iron — canimpart fertility miraculously ? Nobody 
perhaps, seriously entertains such an opinion. Nevertheless, 
the modus operandi of these mechanical operations is by no 
means generally understood. The fact is quite certain, that 
careful ploughing exerts the most favorable influence : the 
surface is thus mechanically divided, changed, increased, 



and renovated ; but the ploughing is only auxiliary to the 
end sought. In the effects of time, in what in Agriculture 
are technically called fallows — the repose of the fields — we 
recognise by science certain chemical actions, which are 
continually exercised by the elements of the atmosphere 
upon the whole surface of the globe. By the action of its 
oxygen and its carbonic acid, aided by water, rain, changes 
of temperature, etc., certain elementary constituents of 
rocks, or of their ruins, which form the soil capable of cul- 
tivation, are rendered soluble in water, and consequently 
become separable from all their insoluble parts. These 
chemical actions, poetically denominated the "tooth of 
time," destroy all the works of man, and gradually reduce 
the hardest rocks to the condition of dust. By their influ- 
ence the necessary elements of the soil become fitted for 
assimilation by plants ; and it is precisely the end which is 
obtained by the mechanical operations of farming. They 
accelerate the decomposition of the soil, in order to provide 
a new generation of plants with the necessary elements in 
a condition favorable to their assimilation. It is obvious 
thai the rapidity of the decomposition of a solid body must 
increase with the extension of its surface; the more points 
of contact we offer in a given time to the external chemical 
agent, the more rapid will be its action. The chemist, in 
order to prepare a mineral for analysis, to decompose it, or 
to increase the solubility of its elements, proceeds in the 
same way that the farmer deals with his fields — he spares 
no labor in order to reduce it to the finest powder ; he sep- 
arates the impalpable from coarser parts by washing, and 
repeats his mechanical bruising and trituration, being as- 
sured his whole process will fail if he is inattentive to this 
essential and preliminary part of it. — Liehig's Letters. 

Having spoken of some of the general principles, let me 
now direct your attention to some of those particulars which' 
will more forcibly exhibit the connection between chemistry 
and agriculture, and demonstrate the impossibility of per- 
fecting the important art of rearing food for man and ani- 
mals without considerable knowledge of our science. It 
has already been remarked, that the great mass of organic 
matter consists of only ybnr elementary bodies, viz : carbon^ 
dxygen, hydrogen, and nitrogen. An important question 
naturally arises, namely : from what source do plants de- 
rive these elements? And first, of carhon. I presume it 
will be conceded that carbon is incapable of entering di- 
rectly, in its solid slate, into the circulation of plants ; since 



8 

solid substances of every kind are unfit for being taken up 
by the organs of plants. Carbon, therefore, must enter ei- 
ther in the gaseous or liquid form, but from what source 
must it be derived ? There are but two sources from which 
it can be obtained — the soil in which the plant grows — and 
the air by which its stem and leaves are surrounded. In 
the soil much vegetable matter is often present, and the 
farmer adds vegetable manure in large quantities with the 
view of providing food for his intended crop. Are plants 
really fed by the vegetable manure that is added to it? 
This question has an important practical bearing. Let us, 
therefore, submitit an examination. 

1st. We have the most conclusive and satisfactory geolog- 
ical evidence, that there was a time when no vegetable 
matter existed in the soil which overspread the earth's sur- 
face. The first plants must have grown without the aid 
of either animal or vegetable matter — that is, they must have 
been nouiished from the air. 

2d. It is known that certain marly soils, raised from 
a great depth beneath the surfiice, and containing no veg- 
etable matter, will yet, without manure, yield luxuriant 
crops. Islands upheaved from the bottom of the ocean by 
subaqueous volcanic action, soon become clothed with veg- 
etation. The carbon in such cases must also have been 
derived from the air. 

3d. You know that some plants grow and increase in size 
when suspended in the air, and without being in coniact 
with the soil. You know, also, that many plants — bulbous 
flower-roots for example — will grow and flourish in pure 
water only, provided they are open to the access of the at- 
mospheric air. Seeds also will germinate, and when daily 
watered, will rise into plants, though sown in substances 
that contain no trace of vegetable matter. These facts have 
been established experimentally by. MM. DeSaussure and 
Boussin2:ault. The source of carbon in these cases cannot 
be doubled. 

4th. When lands are impoverished, they are laid down 
to grass, and the longer they lie undisturbed the richer in 
vegetable matter does the soil become. When broken up, 
a black fertile mould is found where little trace of organic 
matter had previously existed. Tlie same observation ap- 
plies to lands long under wood. The vegetable matter in- 
creases, the soil im^Troves, and cleared and ploughed it 
yields abundant crops of corn. Do grasses and trees de- 
rive their carbon from the soil ? Then, how, by their 



9 

growth, Jo they increase the quantity of carbonaceous mat- 
ter which the soil contains? It is obs'ious ihat, taken as a 
whole, they must draw from the air not only as much as is 
contained in their own substance, but an excess also, which 
ihey impart to the soil. 

5th. But on this point, the rapid growth of peat may be 
considered as absolutely conclusive. A tree falls across a 
little running stream, dams up the water, and produces a 
marshy spot. Rushes and reeds spring up, mosses take 
root and grow. Year after year new shoots are sent forth 
and the old plants die. Vegetable matter accumulates; a 
bog, and finally a thick bed of peat is formed. Whence 
have these plants derived their carbon? The quantity 
■originally contained in the soil is, after a lapse of years, 
increased J.O,()UO fold. Has deatl matter the power of re- 
producing itself? \ou will answer at once, that all these 
plants must have grown at the expense of the air, must 
have lived on th« carbon it was capable of affording them, 
and as the}'' died must have left this carbon in a state unfit 
to nourish the succeeding races. This reasoning appears 
unobjectionable, and, from the entire group of facts, we 
seem justified in concluding that plants ever}" where, and 
under all circumstances, derive the whole of their carbon 
from the atmosphere. — Johnston. 

I shall not pause to point out the limitation of this infe- 
rence — that under certain circumstances the soil docs not 
■cooperate with the air in furnishing this eletnent ; it is suHi- 
cient for our purpose to have established the fact, that 
plants derive tlie greater ■portion of their carbon from the at- 
mosphere. Various experiments and observations prove 
conclusively, that this carbon enters plants in the form of 
carbonic acid. You are aware that this gas is an invariable 
■constituent of the atmosphere; thus vegetables are fur- 
wished with an inexhaustible supply of this element. 

The source of the oxygen and the hydrogen of plants is 
less doubtful, and will r^ijuire less illuslration than that 
•of carbon. Water is a well-known conjpound of these two 
■elements. In the form of aqueous vapor, this compoimd 
-pervades the atmosphere, and plays among the leaves of 
plants, wliile in the liquid state, it is diffused through the 
soil, and is unceasingly absorbed by the roots of all living 
vegetables. Hydrogen is also contained in ammotfia, and 
oxygen enters into the composition of carbonic acid, be- 
sides heiuix a larue constituent of the air itself. From these 



10 

atmospheric source55, it is obvious that an ample supply ai 
oxygen and hydrogen is afforded to plants. 

Finally, it has been abundantly shown by Liebig, Du- 
mas, Boussingault, and others, that the remaining element^ 
nitrogen, is likewise furnished from the atmosphere in the 
forms of ammonia and nitric acid. Hence it follows, that 
the atmosphere contains all the elements which form the 
great mass of organic structures, and that too, in a form fit- 
ted for the assimilation of vegetables. But if the atmos- 
phere furnishes every thing essential to organization, why, 
it may be reasonably asked, is so much attention paid to 
the preparation of the soil and to manuring? Is the agri- 
cultural experience of all ages and of all countries to be at 
once re!Jccted, or are we to modify our views? We here" 
touch upon a point which is of vast importance to the prac- 
tical agriculturist. 

It has been previously hinted, that, in addition ioihejmtr 
organic elements which form the bulk of vegetables, there 
are certain inorganic substances, which, although existing 
in small quantities, play a most important part in their 
economy. It cannot be doubted that the inorganic constit- 
uents contained in the ashes are really essential parts of 
the substance of plants-'^that they cannot live a healthy life 
or perfect all their parts without them— and that it is the 
duly of the husbandman to supply them when they are 
wanting in the soil. In the vast aerial ocean which envel- 
opes our planet, the beneficent Creator has furnished an in- 
exhaustible supply of the rnio materials which are required 
for the development of organized structures; but unless 
the proper machinery and tools are supplied, these mate- 
rials cannot be made to assume an available form. Every 
plant receives, by means of the water taken up by the 
I'ootS) certain soluble alkalies, alkaline earths and phos- 
phates, which are necessary to its organization. If these 
elements be wanting, its growth is retarded. In fact, the 
development of the plant is in a direct ratio to the amount 
of matters which it takes up from the soil. If, therefore, a 
soil is deficient in these mineral constituents^ required by 
plants, the)'^ will not flourish, even with an abundant supply 
of every thing el^e. We have already seen, that the pro- 
duce of carbon is independent of a supply of carbonaceous 
manure, but it depends upon the presence of certain ele- 
ments in the soil which in themselves contain no carbon, 
together with the c^;istencc of conditions under which their 
assimilation byj)lanls can be cficctcd. We increase the 



11 

y>rocluce of our culilvated fields, in carbon, by supplying 
lime, ashes and marl, substances whicli cannot iurnisli car- 
bon to the plants, and 3'et it is indisputable, being tounded 
upon abundant experience, that in these substances we fur- 
nish to the fields elements which greatly increase the bulk 
of their produce, and consequently the amount of carbon. 
If we admit these tacts to be established, we can no longer 
doubt that a deficient produce of carbon, or in other words, 
the barrenness of a field does not depend upon carbonic 
acid, because we are able to increase the produce, to a cer- 
tain degree, by a supply of substanc<!S which do not contain 
any carbon. — Liehlg's Letters. 

The great object of agriculture, therefore, is to discover 
the means best adapted to enable these plants to assimilate 
the carbon of the atmospheie which exists in it as carbonic 
acid. In furnishing plants, therefore, with mineral elements 
we give them the power to appropriate carbon from a 
a source which is inexhaustible ; while in the al)sence ot 
these elements, the most abundant supply of carbonic acid, 
or of decaying vegetable matter, would not increase the 
produce of the field. 

As has already been remarked, all plants require for their 
healthy sustenance the alkalies and alkaline earths, each in 
a certain proportion; and in arldilion to tliese, the ccralia, 
such as corn, rice, wlieat, barley, rye, oats, etc., do not suc- 
ceed in a soil destitute o\' silica in a solubl-e condition, as it 
forms the frame-work of their stems and leaves. The com- 
binations of this substance found as natural productions, 
namely, the silicates, differ greatly in the degree of facility 
with which they undergo decomposition, in consequence of 
the unequal resistance opposed by their integral parts to the 
dissolving power of the atmospheric agencies. Thus, the 
granite from certain localities degenerates into a powder in 
a time which scnreely suffices to deprive other kinds oi their 
polish. Some soils abound in silicates so readily decompo- 
sable, thatever^'' one or two years, as much silicate ot pot- 
ash becomes soluble and fitted for assimilation as is re- 
quired by the leaves and straw of a crop of wheal. In Eu- 
rope, particularly in Hungary, extensive districts are not 
uncommon where wheat and tobacco have been grown al- 
ternately upon the same soil for centuries, the land never 
receiving back any of those mineral elements which were 
withdrawn in the grain and straw. On the oiljer hnnd, 
there are fields in which the necessary amount of soluble- 
silicate of potash for a single crop of wheat is not separated 



12 

from tlie insoluble masses in the soil in less than two, three, 
or even more years. The term fallow, in Agriculture, de- 
signates that period in which the soil, left to the influence 
of the atmosphere, becomes enriched with those soluble 
mineral constituents. FaUoir, however, does not generally 
imply an entire cessation of cultivation, but only an inter- 
val in the growth of the ceralia. That store of silicates and 
alkalies which is the principal condition of their success, is 
obtained, if potatoes or turnips are grown upon the same 
fields in the intermediate periods, since these crops do not 
abstract a particle of silicate, and therefore leave the field 
equally fertile for the following crop of wheat. — Liebig. 

From the preceding remarks it is obvious, that the me- 
chanical working of the soil is the simplest and cheapest 
method of rendering the elements of nutrition contained in 
it accessible to plants. But it may be asked, are there not 
other means of decomposing the soil besides its mechanical 
subdivision ? Are there not substances, which by their 
chemical operation shall equally well, or better, render its 
constituents suitable for entering into vegetable organisms? 
Yes, we certainly possess such substances, and one of then), 
namely, quicklime, has been employed for the last century 
in England for this purpose. In order to obtain correct 
views respecting the effect of quick lime upon the soil, let 
me remind jou of the process employed by the chemist 
when he wishes to bring the elements of a mineral into a 
soluble slate. Let the mineral to be examined be, for in- 
stance, feldspar ; this substance, even when reduced to the 
finest powder, requires for its solution to be treated with an 
acid for weeks or months ; but if we first mix it with quick- 
lime, and expose the mixture to a moderately strong heat, 
the lime enters into chemical combination with certain ele- 
ments of the feldspar, and its alkali (potassa) is set free. 
And now the acid, even without heat, dissolves not only the 
lime, but also so much of the silica of the feldspar as to 
form a transparent jell3% The same effect which the lime 
in this process, with the aid of heat and acid, exerts upon 
the feldspar, it produces when ft is mixed with the 
alkaline argillaceous or clayey silicates, and they are for a 
long time kept together in a moist slate. — Idem. 

A no less favorable influence than that of lime, is exer- 
cised upon the soil of peaty land by the mere act of burn- 
ing it ; this greatly enhances its fertility. In their natural 
state, potter's-clay, pipe-clay, loam, and many different 
modifications ol' clay, may be boiled in concentrated sulphu- 



13 

ric add without sensible change ; bnt if freely burned, ihey 
dissolve in the acid with the greatest facility. These kinds 
of clay belong to the most sterile soils, and yet it contains 
within itself all the constituent elements essential to a most 
luxuriant growth of plants ; but their mere presence is in- 
sufficient to secure this end. The soil must be accessible 
to the atmosphere, to its ox^'^gen, to its carbonic acid ; these 
must penetrate it, in order to secure the conditions necessa- 
ry to a happy and vigorous development of the plant. The 
elements present must be brought into that peculiar state of 
combination which enables them to enter into vegetables. 
Clay is often wanting in these properties; but they are im- 
parted to it by teeble calcination. — Lichig. 

These facts explain in a satisfactory manner, the favora- 
ble influence which 7narl and ashes exert upon most soils. 
The ceralia require the alkalies and alkaline silicates, which 
the action of the lime, marl, or ashes, renders fit for the as- 
similation of the plants. If, in addition to these, there is 
any decaying organic matter present in the soil, supplying 
carbonic acid, it may facilitate their development , but it is 
not essential to their growth. If we furnish the soil with 
ammonia, and the phosphates, which are indispensable to 
the ceralia, with the alkaline silicates, we have all the con- 
ditions necessary to insure an abundant harvest. The at- 
mosphere is an inexhaustible store of carbonic acid. — Idem. 

I have now to make a few remarks on the uses and effects 
of animal and vegetable manures, properly so called. In 
order to understand the nature of these, and the peculiarity 
of their influence upon our fields, it is highly important to 
keep in mind the source whence they are derived. It is 
well known, that during the life of an animal every part of 
its living substance is undergoing a perpetual change ; all 
its component parts, assuming the form of lifeless com- 
pounds, are thrown off by the skin, lungs, and urinary sys- 
tem, altered more or less by the secretory organs. Obser- 
vation and chemical analysis teach us, that the carbon, oxy- 
gen, and hydrogen of the blood, of the muscular fibre, and 
of all the animal tissues which can undergo change, return 
into the atmosphere, through the skin and lungs, in the form 
of carbonic acid and water. The nitrogen, and all the so- 
luble inorganic elements, are carried to the ca7-th in the 
urine. These changes take place in the healthy animal 
body during every moment of life ; a waste and loss of sub- 
stance proceeds continually; and if this loss is to be res- 
tored, and the original weight and substance repaired, an 



14 

adequate supply of materials must be furnished wlience the 
blood and wasted tissues ma^-- be regenerated. This sup- 
ply is obtained from the food. In an adult person in a 
healthy condition, no sensible increase or decrease of weight 
occurs from day to day. In youth the weight of the body 
increases, while in old age it decreases. There can be no 
doubt that in the adult, the food has exactly replaced the 
loss of substance : it has supplied just so much carbon, hy- 
drogen, nitrogen, and other elements, as have passed through 
the skin, lungs and urinary organs. In youth the supply is 
greater than the waste. Partofthe'elements of the food remain 
to augment the bulk oi the body. In old age the waste is 
greater than the supply, and the body diminishes. It is un- 
questionable, that, with the exception of a certain quantity 
of carbon and h3'drogen, which are secreted by the skin and 
lungs, we obtain, in the solid and fluid excrements of man 
and animals, all the elements of their food. Thus we see, 
that all the constituent ingredients of the consumed food, 
soluble and insoluble, are returned ; and as food is prima- 
rily derived from the fields, we possess in those excrements 
all the ingredients which we have taken from it in the form 
of seeds, roots, or herbs. One part of the crops employed 
for fattening sheep and cattle, is consumed by man as ani- 
mal food ; another part is taken directly — as flour, potatoes, 
corn, rice, green vegetables, etc. ; a third portion consists 
of vegetable refuse, and straw employed as litter. None 
of the materials of the soil need be lost. We can, it is ob- 
vious, get back all its constituent parts which have been 
withdrawn therefrom, as fruits, grain and animals, in the 
fluid and solid excrements of man, and the bones, blood and 
skins of the slaughtered animals. It depends upon our- 
selves to collect carefully all these scattered elements, and 
to restore the disturbed equilibrium of composition in the 
soil. We can calculate exactly how much and which of the 
components of the soil we export in a sheep or an ox, in a 
bushel of corn, wheat, or potatoes, and we can discover, 
from the known composition of the excrements of man and 
animals, how much we have to supply to restore what is 
lost to our fields. — Lieb/g^s Letters. 

The principal problem for agriculture is, how to replace 
those substances which have been taken from the soil, and 
which cannot be furnished by the atmosphere. If the ma- 
nure supplies an imperfect compensation for this loss, the 
fertility of a field or of a country decreases ; if, on the con- 
trary, more are given to the fields, their fertilit}^ increases- 



15 

An importation of urine, or of solid excrements, as guana, 
from a foreign country, is equivalent to an importation of 
grain and cattle. In a certain time, the elements of those 
substances assume the form of grain, or of fodder, then be- 
come flesh and bones, enter into the human body, and re- 
turn again day by day to the form they originally possessed. 
The only real loss of elements we are unable to prevent, is 
of the phosphates, and these, in accordance with the cus- 
toms of all modern nations, are deposited in the grave. — 
For the rest, every part of that enormous quantity of food 
which a man consumes during his hfetime, (say 60 or 70 
years,) which was derived from the fields, can be obtained 
and returned to them. — Idem. 

You will now understand that the constituents of the solid 
parts of animal excrements, and therefore their qualities as 
manure, must vary with the nature of the creature's food. 
If we feed a cow upon turnips, or potatoes, without hay, 
straw, or grain, there will be no silica in solid excrements, 
but there will be phosphate of lime and magnesia. In one 
word, the excrements of the animal must contain all the 
constituent elements of food, and therefore are best suited 
to manure the vegetables which it consumed. The excre- 
ments of animals which have been fed on peas'and potatoes 
are principally suited for manuring crops of peas and po- 
tatoes ; of those which have been fed on corn and oats, for 
manuring corn and oats. — Ide7n. 

It is obvious, therefore, that the art of rational agricul- 
ture, must be based upon the restitution of a disturbed equi- 
librium. Can it be imagined that any country, however 
rich and fertile, with a flourishing commerce, which for 
centuries exports its produce in the shape of grain and cat- 
tle, will maintain its fertility, if the same commerce does 
not restore, in some form of manure, those elements which 
have been removed from the soil, and which cannot be re- 
placed by the atmosphere ? Must not the same fate await 
every such country which has actually befallen the once 
prolific soil of Virginia, now in many parts no longer able 
to grow its former staple productions — wheat and tobacco? — 
Liebig. 

When a country is thinly peopled, like the newly settled 
districts of the United States and the greater portion of our 
state, a very defective system of culture will produce food 
enough not only for the wants of the inhabitants, but for the 
partial suppl}'^ of other countries also. But when the pop- 
ulation becomes more dense, the same imperfect or slug- 



16 

gish system will no longer suffice. The land musL be bet- 
ter tilled, its special delects must be studied, and means 
must gradually be adopted for extracting the maximum 
produce from every portion susceptible of cultivation. As 
the population of a country continues to increase, it is an 
important question to determine whether the food raised 
from the land will continue to augment in the same ratio. 
In this country, the population is too sparse to furnish the 
means of making any estimate on this point. With regard 
to England our data are more definite. The superficial 
area of Great Britain comprises about 57 millions of acres, 
of which, in 1840,34 millions were in cultivation, about 13 
millions were incapable of culture, and the remaining 10 
millions were waste lands susceptible of improvement. 
The population in 1840 — or 20 millions — were, therefore, 
supported by the produce of 34 millions of acres ; or every 
34 acres raised food for about 20 people. Suppose the 10 
millions of acres which are susceptible of improvement, to 
be brought into such a state of culture as to maintain an 
equal proportion — the most favorable supposition — they 
would raise food for an additional population of 6 millions, 
or would keep Great Britain independent of any large and 
constant foreign supply till the number of its inhabitants 
amounted to 2G millions. But at the present rate of in- 
crease, this will take place in about 20 years from 1840, so 
that by 1860, unless some general improvement take place 
in the agriculture of the countr^s the demands of the popu- 
lation will have completely overtaken the productive pow- 
ers of the land. — Johnstnji. 

But when we consider the rapid advancement of this de- 
partment of science, it is impossi ble to predict or foresee the 
exact limit of the productive powers of a country, although, 
it is obvious, that there must be a limit to it. 

In the large towns of England, as also of this country, a 
large quantity of the elements of the soil indispensable to 
plants do not return to the fields. By contrivances result- 
irrg from the manners and customs of the people, an enor- 
mous quantity of the phosphates, are daily carried into the 
rivers, in the form of solid and liquid excrements. Hence, 
in England, it has become necessary to import bones to re- 
store this loss. At present, the importation of bones for 
manure amounts in value to upwards of a million of dollars 
per annum, but it is far from being sufficient to supply the 
waste. It has been estimated, that if it were possible to 
restore to the soil of England and Scotland the phosphates 



which during; the last 50 years have been carried iiilo the 
sea by the Tliaines and the Clv'de, it would be et^uivalent 
to manuring with millions oftons ol" bones, and iho produce 
of the land would increase one-third, or periiaps, double it- 
self, in 5 or 10 years. — Llcbig^s Letters. 

When we have exactly ascertained tlie (juantlty ot ashes 
left after the combustion of cultivated plants whieh liave 
grown upon all varieties of soil, and have ol)L:iined correct 
analyses of these ashes, we shall learn with certainty which 
of the constituent elements of the [)lants are constant and 
which are changeable, and we shall arrive at an exact 
knowledge of the sum of all the ingredients we withdraw 
from the soil in the different crops. With this knowledge 
the farmer will be able to keep an exact record of the pro- 
duce of his fields in harvest, hke the account-book of a well- 
regulated manufactory ; and then by a simple calculation 
he can determine precisely the sidistances he must supply 
to each field, and the quantity of these, in order to restore 
their fertility. He will be able to express, in pounds weight, 
how much of this or that clement he must give to the soil 
in order to augment its fertility foran}^ given kind of plants. 
These researches and experiments are the great dc/uhnita, 
of the present time. To the united efForis of the chemists 
of all countries we may ccjnfidenlly look for a solution of 
these great questions, and by the aid of cidightened agricul- 
turists we shall arrive at a rational system of gardening, 
horticulture, and agriculture, ap[)licable to every country 
and all kinds of soil, and which will be based u])()n the im- 
mutable foundation of observed facts and philosophical in- 
duction . — Idem . 



LECTURE II. 



•"•♦e® 



Plants, as we have seen in a former Lecture, derive" 
much of their sustenance from the carbonic acid of the at- 
mos])here ; yet of this gas the air contains only a very small 
fraction, and in so far as experiments have yet gone, this 
fractional quantity docs not appear to diminish. How, then, 
it may be asked, is the supply of carbonic acid kept up? 
Again, plants most probably obtain much of their nitrogen 
either from ammonia or from nitric acid ; and yet, neither 
in the soil nor in the air do these compounds permanently 
exist in any notable quantity. Whence then is the supply 
of these substances brought within the reach of plants? 
The importance of these two questions will appear more 
dislinctl}^ if we endeavor to estimate how much of their 
carbon plants really draw from the atmosphere — and how 
much of the nitrogen they contain must be derived from 
the same source. On this subject, it is, perhaps, impossible 
to obtain perfectly accurate results. Several series of 
trustworthy experiments, however, have been made by M. 
Boussingault, which enables to arrive at very useful ap- 
proximations in regard to the proportion ot their carbon 
which tlioy actually extract from the air by which they are 
surrounded. It is necessary that you should understand 
the principle on which they were conducted, in order that 
you may be prepared to place confidence in the determina- 
tions at which he arrived. Jf we were to examine the soil 
of a field on which we are about to raise a crop of corn — 
and should find it to contain a certain per centage, say 10 
])er cent of vegetable matter, or 5 per cent of carbon; and 
after the crop is raised and reaped, should, on a second ex- 
amination, find it to contain exactly the same quantity of 
carbon as before, we could not resist the conviction, that, 
with the exception of what was originally in the seed, the 
])lant during its growth had drawn from the air all the car- 
bon it contained. The soil having lost none, the air must have 
yicUcil tJic ivJiolc svfphj. Or if, after examining the soil of 
our field, we tnix with it a supply of farm-yard manure, 



19 

containing a known weight, say one ton, of carbon, and 
when the crop is reaped, find as before, that the per cent- 
age of vegetable matter in the soil has sufft3red no diminu- 
tion, we are justified in concluding that the crop cannot, at 
the utmost, have derived from the soil any greater weight 
of its carbon than the ton contained in the manure which 
had been added to it. — BoussingauWs Rural Economy. 

Such was the principle on which Boussingault's experi- 
ments were conducted. He determined the per ceiitage of 
carbon in the soil before the experiment was begun — the 
weight added in the form of manure — the quaniity con- 
tained in the series of crops — and lastly, the proportion of 
carbon remaining in the soil. By this method he found, 
that an acre of land su[iplied with manure containing 2513 
pounds of carbon, produced 7544 pounds of carbon in the 
crops, making the difference, or amount of carbon derived 
from the air 5031 pounds. The crops collected contained 
three times the cjuantity of carbon present in the manyre, 
and therefore, the jilants, during their groivth, must on the whole 
have derived two-thirds of their carbon from the air. It is fair 
to assume that a considerable portion of the carbon of the 
manure and of the soil would naturally escape and be lost, 
and that, tlierefore, the proportion of carbon derived from 
the air in Baussingault's experiments, must have been re- 
ally considerably greater than is indicated by the numeri- 
cal results. However, let two-thirds o^'the entire (juantity 
of carbon contained in a series of crops be taken asilie av- 
erage proportion which must be derived from the air in the 
form of carbonic acid — and let the average weight of the 
dry crop reaped be estimated at one and a half tons per 
acre. Then, if the crop contain half its weiglit of carbon, 
the p\,ants grown on eacfi acre must annually extract from 
the air 10 cwt. or 1120 pounds of carbon in the form of car- 
bonic acid. — Johnston'' s Lectures. 

But the cpiestion will here at once suggest itself to you — 
does not the quantity thus extracted from the air really 
form a very large proportion of the whole weight of carbon 
which is contained in the atmosphere? A sim[)le calcula- 
tion will give us clear ideas in regard to this interesting 
point. The adnfirable researches of De Saussure show, 
that the average quantity of carbonic: acid in the atmos- 
phere of our globe may be estimated at about y^y^^ij-Tj- or -^jon 
part of its entire bulk. This is equal very nearly to j^%-^ of 
its weight. Or taking the whole weight of the atmosphere 
at fifteen pounds on the square inch — that of the carbonic 



20 

acid will be 0.009 lbs. or G;} grains per square inch. But 
as the carbonic acid contains only twenly-seven and two- 
third per cent of its weight of carbon, the weight of this el- 
ement which presses on each square inch of the earth's sur- 
face is only 17.39 grains. Upon an acre, therefore, this 
amounts to 7 tons. But if the crop on each acre of culti- 
vated land annually extracts from the air half a ton of car- 
bon, the whole of the carbonic acid in the atmosphere would 
sustain such a vegetation over the entire globe for fourteen 
years only. And if we even suppose such a vegetation to 
extend over one-hundredth of the earth's surface, it still ap- 
pears sufficient to exhaust the carbonic acid of the air in 
fourteen hundred years. A very short period, compared 
even with ihe limits of authentic history, has yet elapsed 
since experience began to be made on the true constitution 
of the :ilmosphere ; we have no trustworthy data, therefore, 
on which to Ibund a confident opinion in regard to the per- 
manence of the proportion of carbonic acid which it now 
contains. But the recorded identity of all the phenomena 
of vegetation renders it probable that the proportion hasnoi 
sensibly diminished even within historic times. — Idem. 

From what sources, then, is the supply ot carbonic acid 
in the atmosphere kept up? And if the proportion be per- 
mnncnt, by what compensating jirocesses is the quantity 
which is restored to the atmosphere produced and regulat- 
ed ? You are all aware, that all the rain which falls as 
well a^s the watery vapor actually present in the air, may 
fall in the form of rain or dew and ascend again in vapoi 
several successive times in a single year. Is it so also witl; 
the carbon in the air? Does that which feeds the growing 
plant to-day, again mount up in the form of carbonic acid 
at some future time, ready to minister to the sustenance ol 
new races, and to run against the same round of ever-vary- 
ing change? Such is, indeed, the general history of the 
agency ol' the carbonic acitl of the atmosphere; but when 
once it has been fixed in the plant it must pass through 
many successive changes before it is again set free. The 
conditions, also, under which it is restored to the atmos- 
phere are so diversified — and tl/e agencies by which, in 
each case, it is liberated are so very distinct, as to require 
that the several modes by which the carbon of plants is re- 
converted into carbonic acid and returned to the air, should 
be made topics of separate consideration. And 1st, on the 
])rod action of carbonic acid by the respiration of animals. 
The air wc brcaihe when it is draw'n iu/o tjje lungs, con- 



21 

tains 7 jVo^^^ of its bulk of carbonic acid ; when it returns 
again^y-ow the lungs, the bulk of this gas amounts, on an aver- 
age, to one twenty-fifth of the whole; or its quantity is in- 
creased one hundred times. The actual bulk of the carbonic 
acid emitted from the lungs of a single individual in twenty- 
four hours varies exceediugly ; it has been estimated, how- 
ever, on an average, to contain upwards of five ounces of 
carbon. A full grown man, therefore, gives off from his 
lungs, in the course of a year, upwards of one hundred 
pounds of carbon in the form of carbonic acid. If the quan- 
tity of carbon thus evolved from the lungs be in proportion 
to the weight of the animal, a cow or a horse ought to give 
offG times as much as a man. From indirect experiments, 
M. Boussingault estimated the actual quantity of carbon 
lost in this way by a cow and a horse, at six or seven times 
the amount given off from the lungs of a man. If we sup- 
pose each inhabitant of the United States, young and old, 
to expire only eighty pounds of carbon a year, the twenty 
millions would emit seven hundred thousand tons; and, 
allowing the cattle, sheep, and all other animals, to give off 
twice as much more, the whole weight ot carbon returned 
to the air by respiration in this country would be about two 
millions of tons, or the quantity abstracted from the atmos- 
phere by four millions of acres of cultivated land. Extend- 
ing the same calculation to the whole animal population of 
the globe, it appears, that upwards of one hundred millions 
of tons ot carbon is annually supplied to the atmosphere 
through the medium of respiration ; an amount sufficient to 
furnish carbon to the produce of two hundred millions of 
acres of cultivated land. 

Whence is all this carbon derived? It is a portion of that 
which has been conveyed into the stomach in the form of food. 
Suppose the carbon contained in the daily tood of a full- 
grown man to amount to one pound — which is a large al- 
lowance — then it appears that, by the ordinary processes 
of respiration, at least one tldrd of the carbon of his food is dai- 
ly returned into the air. In other animals the proportion re- 
turned may be diflerent from what it is in man, yet the life 
of all depends on the emission to a certain extent, of the 
same gas. And since all are sustained by the produce of 
the soil, it is obvious, that the process of animal respiration 
is one of those methods, by which it has been provided, that 
a large portion of the vegetable productions of the globe, 
should be almost immediately resolved into the simpler 
forms of matter, from which it was originally compounded, 



22 

and again sent up into the air to minister to thn wants of 
new races. 

2. Anotherimportantsourccofcarbonic acid is familiartoyou 
in the results of artificial combustion. Duringthis process, 
the carbon is made to combine with the oxygen of the atmos- 
phere, and the vegetable matter is resolved again into car- 
bonic acid and water. It is impossible to say whet pro- 
portion of the carbon absorbed during the general vegeta- 
tion of the globe, is thus annually restored to the atmosphere 
by the burning of vegetable matter. That it must be very 
great, will appear from the single fact, that by far the 
greater part of the globe is dependent tor its supplv of fuel 
on the produce of its forests. The coal — which, you are 
aware, is of vegetable origin — consumed in Great Britain 
alone is estimated at twenty millions of tons, containing on 
an average at least 70 per cent., or 14 millions of tons of 
carbon. But if the annual produce of an acre of cultivated 
land contain, as we have before estimated, half a ton of 
carbon derived from the air, the coal consumed in that 
country would supply carbonic acid to the crops grown on 
28 millions of acres. Or, since in Great Britain about 34 
millions of acres are in cultivation, the coal they annuallij 
cons2ime iirodnccs a qnantltij of carbonic acid ichich is alone suffi- 
cient to supply food to the crops that groiv upon | of the arable 
land of that country^ — Johnston. 

In connection with this subject, I must draw your atten- 
tion to one interesting, as well as iiDportant, fact. I have 
spoken of coal as a substance of vegetable origin, and there 
is no doubt that all the carbon it contains, once floated in 
the air in the form of carbonic acid. But the period when 
it was so mixed with the atmosphere, is remote almost be- 
yond conception. When, therefore, we raise coal Irom its 
ancient bed and burn it on the earth's surface, ive add to the 
'Carbon of the air a portion ivhich has not 2>^c^'iously existed in 
the atinosplicrc of our time. How interesting it is to contem- 
plate the relations, at once wise and beautiful, by which 
through the operation ot such laws, dead organic matter, 
intelligent man, and living plants, are all bound together! 
The dead tree and the fossil coal lie almost useless things 
in reference to animal and vegetable life — man employs 
tliem in a thousand ways as ministers to his wants, his 
•comforts, or his dominion over nature — and in so doing, 
himself directly, though unconsciously, ministers to the 
wants of those vegetable races, which seem but to live and 
grow for his use or sustenance. 



2'3' 

o. I shall make but a few remarks on the third head, viz ;' 
the production ot" carbonic acid by the natural decay of veg- 
etable matter, as you will readily perceive that it is in re- 
ality a slow combustion. The carbon of a buming body 
unites directly with oxygen and forms carbonic acid. Ire 
the natural process of decay, however, at the ordinary tem- 
perature of the atmosphere, vegetable matter is exposed to 
the action of both air and water; these both co-operate in' 
inducing and carrying on decomposition, and hence car- 
bonic acid is not, as in the case of combustion, the chief or 
immediate result. In the soil the vegetable matter is con- 
tinually undergoing decay, various substances are pioduced 
in greater or less quantity, some solid, some liquid, and 
some gaseous — but all of them are only hastening-— some 
by one road, so to speak, and some by another — towards 
that final destination which sooner or later they are all fated 
to reach ; when, in the form of carbonic acid and water, 
they shall be in a condition to minister again to the nour- 
ishment of all plants. It is upon \\\e final result of this nat- 
ural decay to which all vegetable matter is su-bject-, that the 
carbonic acid of the atmosphere depends for its largest sup- 
plies. The rapidity with which organized bodies perish, 
and become resolved into gaseous compounds, depends 
partly upon the climate and ])artly on the nature of the sub- 
stances themselves — but all hurry forward to the same end, 
and it is with difficulty that we are able for a time to arrest 
or even retard their steps. It is by this perpetual and ac- 
tive obedience of all dead matter to one fixed law, that the 
existing condition of things is maintained. 

4. There is still another source of carbon, viz : the natu- 
ral evolution of carbonic acid in volcanic countries. It is 
exceedingly difficult, if not absolutely impossible, to esti- 
mate the quantity of this gas which rises into the air in such 
circumstances over an extensive tract of country, fractured 
and broken up by volcanic agency — where the outlets are 
numerous, and the rate at which the gas escapes very vari- 
able. That in many localities it must be very great, how- 
ever, there can be no question. In a single volcanic dis- 
trict, the annual evolution of carbonic acid from springs 
and fissures, has been estimated by Bischof at not less than 
100,000 tons, containing 27,000 tons of carbon. It is ob- 
vious, however, that if the Wio/c of the carbon contained in 
the produce of the general vegetation of the globe be ulti- 
mately restored to the air — either by the respiration of ani-- 
mals, by the natural and slow decay of vegetable matter,< 



24 

ttr b}' the more rapid process of combustion — the constant 
addition of carbonic acid from volcanoes, and from the com- 
bustion of fossil coal, should gradually, though slowly, aug- 
ment the proportion of this gas in the air we breathe; un- 
less it be perpetual!}'' undergoing a permanent diminution, 
to at least an equal extent, from the operation of otiier cau- 
ses. Such compensating causes are doubtless continually 
Active on the surface of the earth. It is well established 
that the waters of the ocean absorb a notable amount of 
carbonic acid, which, so far as we know, is not returned, 
at least in our time, to the atmosphere. The waters which 
flow into the sea constantly bear down with them portions 
of animal and vegetable matter, much of which is perma- 
nentlv imbedded in the deposite of clay, silt and sand, 
which are continually in the course of formation. And 
lastly, in man}'' parts of the world, much vegetable matter 
accumulates in the form of peat, becomes buried beneath 
clay and sand, and thus is prevented from undergoing the 
natural process of decay. It is impossible to say how much 
carbon is permanently withdrawn from the atmosj)here by 
these several agencies. There is reason to believe that it 
is quite as great as the quanlily added to the air by the 
combustion of coal, and by the evolution of carbonic acid 
in volcanic districts. — Bischofon Heat of the Globe. 

The neneral coiiclusions, therelbre, which we seem jusli- 
fied in drawing in regard to the suppl}^ of carbonic acid to 
the atmosphere are as follow : 

1. That a large portion of the carbonic acid absorbed by 
plants is imimedintcly and directly restored to the air by 
the respiration of the animals which feed upon vegetable 
productions. 

2. That a still larger portion is more slowly returned by 
the gradual reconversion of vegetable substances into car- 
bonic acid ana water duiing the process of natural decay. 

3. That vcarJij all the remainder is given back in the re- 
sults of ordinary combustion. 

4. That a further j^ortion, which has not previously exist- 
ed in the atmosphere of our time, is conveyed to it by the 
burning of fossil fuel, and bv llie emission of carbonic acid 
from cracks and fissures in the surface of the earth ; yet 
that the (juantily thus added cannot be supposed to exceed 
that which is constantly and pcrju/inciitli/ separated from the 
atmosphere by other causes. M;my have thought it to be 
Somewhat less, and that, consecjuenlly, the carbonic acid 
is slowly diminishing; we have, however, no satisfactory 



So 

evidence either from theory or experiment, that it has un- 
dergone any appreciable diminuti(in since man has become 
an occupant otthis planet. — Johnston, op. clt. supra. 

We have already shown that an immense amount of car- 
bon is converted into carbonic acid during the processes of 
animal respiration and artificial combustion. Of course 
this must be accomplished at the expense of the oxygen of 
the atmosphere. Chemistry informs us, that as carbonic 
acid consists of 73 per cent, of oxygen, it must require 
about 2Q)Q millions of tons of oxygen, to convert the 100 
millions of tons of carbon which men and animals are an- 
nually throwing oft' from their lungs, into carbonic acid. 
The immense amount withdrawn by combustion is not ta- 
ken into this calculation. You are, doubtless, ready to ask, 
whether this enormous abstraction of oxygen does not di- 
minish the amount of this gas in our atmosphere, and thus 
render the air unlit for the respiration of man and animals ? 
A little calculation will place this question in the proper 
liG;ht. You will recollect that the wei2;ht of the whole at- 
mosphere is equal to 15 lbs. on every square inch of the 
surface of the earth: the oxygen in it constitutes 21 per 
cent of its bulk, or about 2-3 per cent of its weight ; hence 
it follows that the weight of the oxygen is nearly 3i lbs. on 
every square inch. The pressure, therefore, npop an acre 
amounts to 9, SOI tons, and apon a square mile 6,272,040. 
Estimating the superficial extent of our globe at 197i mil- 
lions of square miles, it follows that the weight of the whole 
of the oxygen in the atmosphere is nearly 1,239 billions of 
tons ! Hence it appears, thai 4^ millions of years would be 
required for man and animals, abstracting it at the rate of 
266 millions of tons per annum, to exhaust all of the oxygen 
from the air! ! The amount cousumed in combustion has 
not been taken into this calculation ; but it is obvious, that, 
exaggerating all the data, not less than 800,000 years would 
be required for the animals living on the surface of the 
earth to consume the oxygen entirely. Consequently, if 
we suppose that an analysis of the air had been made in 
1800, and there were no causes in action to replace the oxy- 
gen abstracted from it during the entire centur}", the ani- 
mals at the same time all continuing to live, the analyst in 
1900 would find the oxygen of the air diminished by goVo^h 
of its weight; a quantity which is beyond the reach of our 
most delicate methods of observation, and which, assuredly, 
would have no influence whatever on the life of animals or 
plants. In regard to the permanence of the composition of 



26 

the air, we may sa}' wilh confidence, that the proportion at 
oxygen is secured ibr many centuries; yet as it is not in- 
exhaustible, it is interesting to inquire whether Nature has 
not furnished the means of replacing that which has been 
abstracted, and thus securing an exact compensation? — ■ 
You will anticipate me, when I say, that such a compen- 
sation has been provided, in the peculiar relations of the 
functions of vegetables and animals, which retains the at- 
mosphere in a condition of eternal identity of constitution. 
The growing plants in appropriating the carbonic acid 
which is emitted by animals, decompose it, and liberate an 
equal volume of ox3'gcn. It is obvious, therefore, that alt 
ot the oxygen consumed by animals, is returned to the at- 
mosphere in the process of eliminating carbon by plants; 
the 100 millions of tons of carbon annually taken up by 
vegetables from animals, furnish the air with 266 millions 
of tons of oxygen — precisely the amount abstracted by an- 
imals. 

Animals continually produce carbonic acid, water, am- 
monia — plants incessantly consume ammonia, water, car- 
bonic acid. What one class of beings gives to the air, the 
other takes back from it; so that to take these facts at the 
loftiest point of view of terrestrial physics, we must say 
that, as to their truly organic elements, plants and animals 
spring from the air — are nothyig but condensed air. To 
enable vegetables to effect the reduction of carbonic acid, 
water, and ammonia, another agent is brought into action — • 
it is solar Light. Through her influence, the carbonic acid 
yields its carbon, the water its hydrogen, and the ammonia 
its nitrogen. These element* unite, organized matters 
form, and the earth puts on its rich carpet of verdure. It is 
a circumstance well worthy of interest, that the green 
leaves of plants absorb the chemical rays of the sun so 
completely, as to give no image in the Dagurreolype ; an 
extraordinary absorption doubtless, but which explains 
without difficulty the enormous expense of chemical force 
necessary for the decomposition of a body so stable as car- 
bonic acid. — Dumas. 

The light of the sun, in the existing economy of nature, 
is indeed equally necessary to the health of plants and of 
animals. The former become pale and sickly, and refuse' 
to perform their most important chemical functions when 
excluded from the light. The bloom disappears from the' 
human cheek, the body wastes away, and the spirit sinks, 
when the unhappy prisoner is debarred from the sight of 



27 

the blessed sun. In lils system, too, the presence of light 
is essential to the performance of those chemical functions 
on whicli the healthy condition ot the fluids depends. The 
atmosphere appears to us as containing the primary sub- 
stances of all organization. In aid of it comes light, and 
developes the vegetable kingdom — immense producer of or- 
ganic matter — plants absorb the chemical force which they 
derive from the sun to decompose carbonic acid, water 
and ammonia ; as if they realized a reducing apparatus 
superior to all those with which we are acquainted ; for 
none of these would decompose carbonic acid in the cold. 
Next come animals, consumers of matter and producers of 
heat and force, true apparatus for combustion. We are not 
stopped by the expression co/d-hloodcd animale, wliich would 
seem to designate some animals destitute of the properly 
of producing heat. Iron, which burns vividly in oxygen, 
produces a heat which no one would deny; but reflection 
and some science is necessary in order to perceive, that 
iron which rests slowly in the air disengages quite as much, 
although its temperature does not sensibly var}'. No one 
doubts that lighted phosphorus in burning produces agreat 
quantity of heat. [Jnhindled phosphorus also burns in the 
air, and yet the heat which it develops in this stale was for 
a long time disputed. So as to animals, those which are 
called warm-blooded burn tnuch carbon in a given tiine, 
and preserve a sensible excess of heat above surrounding 
bodies ; those which are termed cold-blooded bur i much 
less carbon, and conse(uientlv retain so slight an excess of 
heat, that it becomes difficult to observe it. But neverthe- 
less, reflection shows ms that the most constant character 
of animal existence resides in this combustion of carbon, 
and in the development of carbonic acid which is the result 
ot It. Whether the question be of superior or inferior ani- 
mals ; whether this carbonic acid be exhaled from the lungs 
or from the skin, does not signifv' ; it is always the same 
phenomenon, the same function. 

It is in animals undoubtedly that organized matter puts 
on its highest expression. But it is not without sufTering 
from it that this change is eflected. The brute matter, or- 
ganized by slow degrees in plants, comes, then, to perform 
its part in animals, and serves as an instrument for sensa- 
tion and thought ; then vanquished by this eflbrt and bro- 
ken, as it were, it returns brute matter to the great reser- 
voir whence it came. Borrowing from modern sciences an 
image of sufficient magnitude to bear comparison with 



28 

these great phenomena, I should Hkcn the existing vegeta- 
tion — truly a storehouse in whicli animal life is fed — to that 
other storehouse otcarbon constituted of the ancient depos- 
its of coal, and which, burnt by the genius of Papin and of 
Watt, also produces carbonic acid, water, heat, motion — 
one might almost say life and intelligence. And if we add 
to this picture, already, Irom its simplicity and its grandeur, 
so striking, the indisputable function of the solar light, 
which alone has the power of putting in motion this im- 
mense apparatus, we shall be struck with the import of 
these woids of Lavoisier; "Organization, sensation, spon- 
taneous movement, life, exist only at the surface of the 
earth, and in places exposed to light. It would seem that 
the fable of the torcli of Prometheus was the expression of a, 
philosophic truth which had not escaped the ancients. — -. 
Without light, nature was without life, and was dead and 
inanimate: by the gift of light, a beneficent God spread 
upon the surface of the earth organization, feeling and 
tl]ought." These words are as true as they are beautiful. 
If feeling and thought, if the noblest faculties of the' soul 
and of the intellect, have need, for their manifestation, of a, 
material covering, to plants is assigned the framing of its., 
web with the elements which they borrow from the air, and 
under the influence of the light which the sun, its inexhausr 
tible source, pours in unceasing floods upon the surface of 
the globe. And as if, in these great phenomena, all must 
be connected with causes which appear the most distant 
from them, we must moreover remark how the ammonia, 
the nitric acid, from which plants borrow their nitrogen, are 
themselves partly derived from the action of the great elec- 
tric sparks which flash forth in stormy clouds, and which — 
furrowing the air through a vast extent — produce there the 
nitrate of ammonia which analysis detects in it. Thus, 
from the craters of those volcanoes whose convulsions so 
often agitate the crest of the globe, continually escapes 
carbonic acid, the principal nutriment of plants ; from the 
atmosphere flashing with lightnings, and from the midst of 
the tempest itself, there descends upon the earth the other 
and no less indispensable nutriment of plants, that whence 
they derive most of their nitrogen, the nitrate of ammonia, 
contained in the thunder-showers. 

To sum up, then, we have seen that plants constitute an 
immense apparatus for reduction, in which is habitually 
created true organic matters fit for the assimilation of ani- 
mals. On the other hand, animals constitute an immense 



29 

apparatus for combustion — reproducing the elements, which 
are returned into the air and the earth. Thus, it is in the 
vegetable kingdam that the great laboratory of organic life 
resides ; there it is that the vegetable and animal matters 
are formed, and they are produced at the expense of the 
air and inorganic constituents of the soil. From plants, 
these matters pass ready-formed into the herbivorous ani- 
mals, which destroy a portion of them, and accumulate the 
remainder in their tissues: — From these, they pass unal- 
tered into the carnivorous animals, who destroy or retain 
some of them according to their wants. Lastly, during the 
life of these animals, or after their death, these organic 
matters, as they are destroyed and resolved into their ulti- 
ijiate elements, return to the atmosphere and to the earth — 
the reservoirs whence they proceeded — to be again used 
in perpetuating the mysterious cycle of organic life on the 
surface of our planet. It is thus, that the grand " Physio- 
logical Balance" in organized beings — so eloquently illus- 
trated by M. Dumias — is maintained : — adaptations, adjust- 
ments, reciprocal dependence of parts, and conformity of 
arrangement, appear everywhere pervading both systems; 
checks and compensations are perpetually in operation, 
which must maintain the equilibrium between the king- 
doms of organic nature — ^just as the masses of the planets 
- — the eccentricities of their orbits — the direction of their 
motions — and the inclinations of the planes in which they 
revolve, are all arranged so as, according to the beautiful 
theorems of Lagrange and Laplace, to preserve the stabili- 
ty of the solar system, by afhxing limits, maxima and min- 
ima, between which the irregularities oscillate. 

To my mind, nothing can exceed the beauty of the con- 
trivance, the exquisiteness of the adaptation. Equally kind 
and bountiful, yet provident, is nature in all her operations, 
and through all her works. Neither skill nor materials are 
ever wasted ; and yet she ungrudgingly dispenses her 
favors, apparently without measure — and has subjected 
dead matter to laws which compel it to minister, and 3'et 
with a most ready willingness, to the wants and comforts 
of every living thing. And how unceasingly does she press 
this her example not only of unbounded goodness, but of 
universal charit3% on the attention of the man of science. 
Does the corn spring more freshly when scattered by a 
Christian hand ? Are the harvests more abundant on a 
Protestant soil? And does not the sun shine alike, and the 
dew descend, on the domains of each political party ? So 



80 

science, from her daily converse with nature, fails not soon^ 
er or later, to take her hue and color from the perception 
of this universal love and bounty. Party and sectarian 
differences dwindle away and disappear from the eyes of 
him who is daily occupied in the contemplation of the 
boundless munificence of the great Impartial ; he sees him- 
self standing in one common relation to his fellow men, and 
feels himself to be most completely performing his part in 
life, when he is able in any way or in any measure to con- 
tribute to the general welfare of all. It is in this sense too 
that science, humbly tracing the footsteps of the Deity in 
all his works, and from them deducing his intelligence and 
his universal goodness — it is in this ser^se, that science is of 
no sect, and of no party, but is equally the province, and 
the property, and the friend of all. 



















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